Vertical Variations of Cloud Microphysical Relationships in Marine Stratocumulus Clouds Observed During the ACE-ENA Campaign

This study examines the vertical variations of cloud microphysical relationships and their implications to cloud microphysical processes in marine stratocumulus clouds using in-situ aircraft observations during the Aerosol and Cloud Experiments in Eastern North Atlantic (ACE-ENA) field campaign. A new diagram with a coordinate system based on cloud droplet liquid water content (L_c) and phase relaxation time scale is proposed to investigate mixing mechanisms. This new diagram analysis shows that the inhomogeneous mixing trait is dominant near the cloud top, but homogeneous mixing trait is stronger at lower altitudes. The relevant scale parameters (i.e., transition length scale and transition scale number) also indicate a high likelihood of inhomogeneous mixing. The relationship between L_c and standard deviation of droplet radius (σ_R) clearly shows the vertical transition: the correlation between L_c and σ_R is positive at lower cloud altitudes, but it becomes negative as altitude increases. Such a vertical transition is consistent with the vertical circulation mixing, modulating the cloud microphysical relationships to suggest homogeneous mixing at a significant depth from the cloud top.